Swab



Feb. 14, 1939. v R. A. WILSON 2,147,072

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Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE 4 Claims.

The invention relates to an improvement in well swabs and particularly to a swab wherein a maximum of production is obtained while causing a minimum of friction against the tubing through which the swab is being moved.

It is one of the objects of the invention to design a .swab rubber in such a manner that a differential pressure between the inside and outside forces Will be obtained which will control the expansion of the rubber to form a seal against the tubing. Another object Vof the invention `is to provide a swab having a rubber which is confined by retaining cups in such a manner that the rubber may have limited expansion.

Another object of the invention is to provide a swab rubber having an area on the outside which is exposed to the swabbed liquid which is somewhat less than the inside area which is subject to expansion and which is also exposed to the pressure of the swabbed liquid.

A still further object of the invention is to provide a swab rubber having an outwardly flaring surface which terminates in a line contact with the tubing so that a minimum of friction occurs.

A still further object of the invention is to control the expansion `of the swab rubber in accordance with the pressure occurring thereon so that a proper seal will be obtained to effect the lifting of the liquid.

Other and further objects of the invention will be readily apparent when the following description is considered in connection with the accompanying drawing, wherein: Y

Fig. l is a central vertical section of a swab positioned in the well tubing in operative position.

Fig. 2 is an enlarged detail View showing the exact construction of the parts.

As is well understood in the art, a swab is lowered into the well bore for `the purpose of raising iluid therefrom and for also creating a suction upon the producing formation. The swab is usually lowered-into apipe or tubing which is illustrated generally at 2. This tubing may be of any length depending upon the depth of the well. The swab itself is indicated generally at Y3 and is suspended by a head 4 which may have a cable or string of rods connected thereto. It is by means of this head that the swab is lowered into and raised from the well. If desired a swivel connection 5 may be provided between the head 4 and the body 6 of the swab.

The body 6 is in the form of a pipe or tube (otitis-*225).

of su'icient length to support the parts and has a central passage 'I therein for the liquid. On the'lower end of the body a nipple 9 is 4connected which carries the valve housing II and .a 'charge of liquid is trapped in the area I5 above the swab in the tubing because the valve I2 closes bygravity as soon as the downward movement of the swab ceases. Stop pins I'I are arranged to limit the opening movement of the valve I2..y

When the swab starts upwardly it is then that a seal must be maintained between the swab and the tubing 2. To effect this seal a base or bottom cup 20 is slidably mounted on the body 6 and is received -upon a supporting ring 2|. This cup has an upwardly and outwardly iiaring lip 22 to form a socket 23 in which the swab rubber 24 is to be seated. An upper cap or cup 26 is also slidably mounted on the body 6 to receive the upper end of the swab rubber 24. This cup has a downwardly extending skirt Z'I which confines the upper end 28 of the swab rubber and is ared at 29 to terminate in the lip 30.

Between these cups 20 and 26 the swab rubber 24 is positioned. 'I'his rubber is of special design in order to accomplish the purposes in view. The upper end of the rubber is cylindrical at v28 and is received inside of the cup 26 so that regardless of the amount of expansion 35 .of the rubber the upper end can not be pulled out from under this cup 26. Below the cylindrical portion 28 a downwardly and outwardly flared face 32 has been formed. This face 32 merges with an upwardly and outwardly flaring face 33 to form an apex 34. The apex is in the form of a circumferential line around the rubber. This is of advantage because under proper pressure control a line contact forms the best seal with a minimum of friction against the tubing.' 45

The inside of the swab rubber is hollow so that it is received over the body 6 and may be formed on its inner surface with a plurality of cylindrical faces such as 35 and 36, which have different diameters. These different cylindrical 50 faces may be joined by a shoulder 31. The body -6 adjacent the elevation which is to be occupied by the swab rubber 24 is providedwith a plurality of openings 38 so that the uid pressure occurring inside ofthe swab will be exerted against 55 the inside cylindrical faces 35 and 36 of the swab rubber. These pressures tend to cause expansion of the swab rubber between the cups 20 and 26 so as to press the rubber outwardly against the tubing and obtain a sealing action.

One of the principal features of the invention is the particular design of the inside and outside areas which are exposed to the pressure of the swabbed liquid so that the movement or expansion of the swab rubber may be accurately accomplished. The outside area or surface which is exposed to the swabbed fluid will be that area between the lower end 4I of the lip 30 on the cup 25 and the apex line at 34. 'I'his area is frustoconical in shape having a length equal to the distance between the apex 34 andthe lip 4l, and circumference equal tothat of the outer periphery of the swab rubber. Of course, the lower or downwardly flaring face 33 is not exposed to the pressure of the liquid being swabbed because the apex line 34 forms a seal with the tubing. The pressure on this area, which will be designated as the area A, will tend to compress the swab rubber and force it away from the tubing.

Opposing this pressure, tending to collapse the rubber, will be the pressure against the inside cylindrical faces 35 and 36 or so much of those faces as may be positioned between the elevation of the lip 4I and the edge 42 of the lip 22 on the lower cup 20. This distance is indicated between the arrows in Fig. 2, and the area which is'thus available to cause expansion of the swab rubber is designated as the area B. This areal is computed as the combined area of the cylindrical faces 35 and 36 between the elevations of the lips 4l and 42.

. It has been found in actual practice that by designing the area B to somewhat extend the area A a differential pressure is obtained which causes satisfactory operation of the swab. Where the usual types of swabs have been completely destroyed or worn out after swabbing one or two wells, swabs employing the present invention have successfully swabbed as many as ten or twelve wells and were still in condition to render additional service.

The differences between the areas A and B will vary to some extent with the size of the swab constructionbecause of differences in the pressures necessary to cause expansion of the rubber, it being understood that thelarger sizes embody thicker and heavier rubbers than do the smaller sizes. For purposes of illustration differences in the areas A and B as great as twentyfive percent have been found to be satisfactory. In operation when the swab starts upwardly the valve I2 will trap the uid which has passed through the swab and the pressure of this liquid being swabbed is exerted on the areas A and B. Because of thefact that the area B is greater there will be a slight expansion of the swab rubber to cause'it'to engage the tubing and form a seal. This differential pressure however is not sufficient to cause undue distortion of the rubber nor to force it against the tubing to such an extent that it will wear or burn away by excessive friction against-the tubing. Another advantage of the present construction is that in lowering the swab into the well the rubber is more or less collapsed and very little wear is caused by its contacting the tubing on the downward trip.

There will be some slight movement of the upper cup 26 but any variation in the exposed area caused by this movement has not been found to be detrimental.

What is claimed as new is:

l. A` well swab comprising a body, a passage therethrough for the liquid being swabbed, openings through said body communicating with the aforesaid passage, a support cup on said body below said openings, a valve insaid pipe below said openings, a swab rubber supported in said cup and extending upward past said openings, an imperforate hold-down cap for said rubber slidably mounted on said body and having a cylindrical surface adapted to receive the upper end of said swab rubber, an inner cylindrical surface on said rubber at the lower end thereof which engages with said body, and a second inner cylindrical surface on said rubber of greater diameter than said first mentioned surface, said second surface extending to the upper end of said rubber and forming a space which communicates with the inner ends of said openings.

2. A swab for wells comprising a body, a sup port cup thereon, a swab rubber in said cup, an imperforate hold-down cap for said rubber slidably positioned on said body, a cylindrical outer surface on the upper portion of said rubber which engages with a cylindrical surface in said cap, a downwardly and outwardly flaring face on said rubber below said cap exposed to the pressure of the liquid being swabbed, an inner peripheral surface on said rubber at the lower end thereof which engages with said body, and `a second inner peripheral surface on said rubber spaced from said body and exposed to the 'pressure of the liquid being swabbed, said second inner surface extending from said first mentioned inner surface to the upper end of said rubber. Y Y

3. A well swab including a body, a pair of spaced imperforate cups thereon, a swab rubber disposed between and extending into said cups, a cylindrical outer surface on the upper end of said rubber which engages with a cylindrical surface in the upper of said cups, oppositely flaring faces on said rubber between said cups which converge to an apex adapted to contact the tubing to form a seal, an inner peripheral surface on said rubber at the opposite end of said rubber from said outer cylindrical surface which engages with said body, a second inner peripheral surfaceon said rubber spaced from said body and exposed to the pressure of the fluid being swabbed, said second inner surface extending from said first mentioned inner surface to the opposite end of said rubber.

4. A swab comprising a stem, a support cup on said stem, a swab rubber surrounding said stem and having inner and outer surfaces closely engaging said stem and cup respectively, a cylindrical outer surface on the upper portion of said rubber, a hold-down cap slidably positioned on said stem and having a cylindrical inner surface engaging the upper end of the rubber, an inner cylindrical surface within the upper portion of the rubber of greater diameter than the stem whereby an annular chamber is provided between the stem and said surface, and openings through said stem tosaid chamber.

ROBERT A. WILSON. 

